It is known to treat certain respiratory problems, particularly asthma, with a pharmacologically active compound which is in a finely divided particulate form, and which is administered by inhalation. One known inhaler for dispensing such material is shown in UK Patent specification No GB2178965 (Glaxo Group Limited), and comprises a circular carrier which includes a number of blisters in each of which a respective dose of material is encapsulated. When a dose is to be administered, a user moves a slider which operates indexing means for bringing the blisters in succession into registry with an airway. The user then pivots a separate handle which ruptures the blister in registry with an airway to allow the medicament therein to be self administered by the user inhaling through a mouthpiece which communicates with the airway.
However, if a user operates the piercing and indexing mechanisms a number of times without inhaling through the mouthpiece, medicament can build up in the airway which results in the user taking too large a dose when he or she next inhales on the mouthpiece.
In addition, the need to operate the indexing means and the piercing mechanism separately can make the device awkward to use.